The present invention relates to a process for preparing halogenated rubbery copolymers of ethylene, at least one other .alpha.-alkene, dicyclopentadiene and optionally one or more other polyenes.
Rubbery copolymers of ethylene, at least one other .alpha.-alkene and at least one polyene have been known to the art for a considerable period of time. These copolymers, generally called EPDM polymers or, more shortly, EPDM, are normally composed of ethylene, propylene, and/or butylene-1, and one or more polyenes, such as hexadiene-1,4, 5-ethylidene norbornene-2 and dicyclopentadiene. The EPDM polymers, unlike any other elastomers, have excellent resistance to oxidation and the action of ozone.
Admixing EPDM, particularly EPDM wherein the polyene is dicyclopentadiene, with diene rubbers, such as polyisoprenes, polybutadiene, and styrene-butadiene copolymers, results in a considerable improvement of the generally low ozone resistance of the diene rubbers. Unfortunately, however, the ozone resistance improvement is generally achieved at the cost of a decrease of the physical and mechanical properties of the resulting vulcanization. This decrease of physical and mechanical properties of the vulcanizates is believed due to the low compatibility of EPDM and the diene rubber, which low compatibility is possibly due to the low degree of unsaturation of the EPDM polymers (whose polyene content is normally no greater than 1-5% by weight) and to the slow curing rate of EPDM. It is known that halogenated rubbery copolymers of ethylene, at least one other .alpha.-alkene, and at least one polyene possess a higher curing rate, and that the presence of the halogen in the copolymer results in a distinct improvement in the compatibility of the EPDM and the diene rubber during covulcanization.
The prior art has proposed several processes for the preparation of halogenated rubbery copolymers of ethylene, at least one other .alpha.-alkene and at least one polyene, but all of these processes proposed by the prior art have one or more drawbacks. For instance, it has been proposed that halogenated EPDM polymers be prepared with the aid of organic halogenating agents which are mixed with the solid polymer, such as, for instance, by milling, after which the admixture is heated to a temperature above 100.degree.C for a considerable period of time. Another proposal is to react such organic halogenating agents at a temperature above 100.degree.C with EPDM dissolved in an organic solvent. If the reaction mixture is exposed to UV irradiation, the temperature may be reduced to the range of 65.degree.-80.degree.C. These processes have the drawbacks that organic halogenating agents are expensive and that the decomposition products of the organic halogenating agents are difficult to isolate from the polymer. Furthermore, the halogenation occurs only at relatively high temperatures, which results in considerable gel formation.
It has also been proposed to use molecular halogen in the preparation of halogenated EPDM, with the halogen contacting the EPDM dissolved in an organic solvent at a temperature above 100.degree.C. Again, if the reaction is conducted with exposure to UV light, the temperature may be reduced to the range of 65.degree.-80.degree.C.
It has also been proposed that brominated EPDM be prepared by reacting molecular bromine at a temperature of -30.degree. - 80.degree.C with EPDM dissolved in an inert organic solvent. It has also been proposed that EPDM be chlorinated with molecular chlorine at a temperature below 80.degree.C. In this latter instance, the EPDM polymers contain termonomers of a special type, which type does not include dicyclopentadiene.
It should be noted that in the above described processes for the preparation of halogenated EPDM polymers, the processes wherein the EPDM is halogenated in the form of a solution in an organic solvent has the additional drawback that the halogenation is normally conducted under such conditions that a portion of the organic solvent also is halogenated. This solvent halogenation can be avoided by performing the halogenation in halogenated organic solvents, such as carbon tetrachloride, but this approach also has disadvantages. The EPDM is normally prepared in organic solvents which are not halogenated, which results in a situation wherein it is necessary to first isolate the EPDM from the solvent used in the polymerization, and then to incorporate the EPDM in the halogenated organic solvent. It will be clear that this is a costly approach, especially since the EPDM has a slow rate of dissolution in all organic solvents.